1. Field of the Invention
This invention relates to a fuel vapor handling system for handling fuel vapor present in a fuel tank, and more particularly to a system equipped with a leak check device which detects a vapor leak in a passage including the fuel tank.
2. Description of Related Art
There has been known the adoption of a canister which traps fuel vapor for the purpose of preventing the discharge of the fuel vapor out of the fuel tank. Furthermore, also known is a fuel vapor handling system which is designed to drive out the fuel vapor trapped in the canister, to thereby supply the fuel vapor through an engine intake passage into the engine, in which the fuel vapor is combusted. This system is also called a fuel vapor purge system.
In the fuel vapor handling system, it is important to detect a vapor leak in the passage of the system in order to prevent the discharge of the fuel vapor. The leak can be detected on the basis of a pressure variation by for example monitoring a pressure in the passage. This leak detection can be conducted for example during engine operation. During engine operation, however, it is difficult to ensure stability suitable for leak detection because of changes in the operating condition of the engine and the movement of a motor vehicle. On the other hand, leak can be detected while the engine is at a stop. The detection of vapor leak executable after stopping the engine has been disclosed in U.S. Pat. No. 5,263,462 for example. However, even after the engine is stopped, there occurs an event which disturbs leak detection, such as the opening of a filler cap of the fuel tank to fill the fuel to the engine.